This invention relates to gas discharge apparatus and, more particularly, it is concerned with an improved means for producing a gaseous plasma facilitating efficient and uniform conversions during heterogeneous (gas-solid) reactions.
In U.S. Pat. No. 3,619,403, assigned to LFE Corporation, there is disclosed improved apparatus for inducing reactions between a material and activated (excited) species of a gas. As described therein, a gas is fed into a reaction chamber at a low pressure and is activated by means of an electromagnetic field formed about a conventionally-wound coil which envelops the material-handling zone of the chamber. During reaction with the activated gas stream (plasma) the material decomposes and/or volatilizes. The resultant byproducts, along with other gaseous constituents, are withdrawn from the chamber by means of a mechanical vacuum pump.
Gas reaction systems of the type described above are being used to great advantage in a variety of industrial processes including, for example, the process of manufacturing integrated circuit components from semiconductor substrates. Such systems provide an economical, safe, and rapid means for selectively removing exposed layers of material from predetermined areas during the various steps involved in the manufacturing process. However, a basic problem encountered with such systems has been their inability to render a sufficiently uniform distribution of reactive chemical conversions throughout the material-handling zone required for production-sized batches of such substrates. Consequently, some of the semiconductor substrates are overexposed to the plasma environment, causing degradation of material and malfunctioning of the final device.
In U.S. Pat. No. 3,705,091 issued to the present inventor and assigned to LFE Corporation, there is disclosed an improved apparatus of the aforementioned nature. This patent discloses, inter alia, a unique coil arrangement about the reaction chamber which produces a substantially uniform distribution of active species throughout the material-handling volume within the chamber. Although chemical conversions occur significantly more uniformly throughout production-size batches of material with this coil arrangement, it has been found that unskilled operators sometimes spend a considerable amount of time in optimizing the system parameters; e.g., rf power, reaction pressure, and their unique combinations, for the quantitative and qualitative variances encountered in different batches of substrate material.
Accordingly, the general object of the present invention is to provide a further improved apparatus of the aforementioned character, whereby uniform heterogeneous reactions are accomplished throughout the material-handling volume of a reaction chamber regardless of operator's skill, and functionally independent of the nature of the substrate material.